The present invention relates to improvements in laminations for use in transformers, constant voltage regulators, chokes, electric motors and/or other static or dynamic electric machines. The invention also relates to a method of making such laminations.
It is already known to hold together a stack of laminations which are to form an iron core or the like by resorting to a suitable adhesive. In accordance with a presently known proposal, the laminations constitute stampings which are obtained from sheets of metallic material and both sides of each stamping are coated with an adhesive substance. The stampings are stacked to form cores of desired height, and the bonding operation is carried out by the application of mechanical pressure and heat. In such cores, the adhesive coats must also perform the function of insulators which can create problems when the stampings exhibit projections which are likely to penetrate through the adjacent adhesive coats and to establish electrical connections between neighboring stampings. The projections can develop as a result of buckling or bending of the metallic sheet material, in the course of stamping and/or as a result of cutting. Direct contact between neighboring stampings entails eddy current losses in the core with adverse influence upon the no-load current as well as magnetic hysteresis losses.
In accordance with another prior proposal in connection with the making of laminated cores for electric machines which must satisfy higher standards regarding their electrical and/or electromagnetic properties, both sides of each metallic layer or lamination are coated with a special insulating material. The insulating material is applied to both sides of a sheet metal blank which is thereupon converted into a plurality of laminations in a stamping machine. The thus obtained laminations are stacked to form a core and are bonded to each other by resorting to a casting resin which fills the gaps between neighboring laminations. A drawback of cores which are assembled of such laminations is that their mechanical stability does not suffice under certain circumstances, e.g., when the machine embodying one or more laminated cores is subjected to dynamic stresses such as vibrations. In order to enhance the mechanical stability of such cores, it is known to surround them by bandages and/or to resort to rivets, screws and/or other types of fasteners. This complicates the making of cores and contributes significantly to their manufacturing cost.
In accordance with still another prior proposal, both sides of each lamination are coated first with an insulating material and each of the thus obtained insulating coats is thereupon coated with an adhesive substance. Such proposal also exhibits the drawback that the laminations and the laminated cores are quite expensive and that the making of such laminations consumes much time.